Chipper machines are used to cut wood into smaller pieces, such as wood chips (“chips”). Chipper machines come in different sizes according to the needs of the installation where they are used. Chipper facilities are large in area and capable of receiving large amounts of raw material. These facilities are typically the first phase of a pulp mill production process.
The raw material fed to the chipper machine is generally logs or other wood material. Raw material or feed material (for simplicity, the raw material will be referred to as “logs,” but could have other shapes) is generally fed continuously into a chipper machine. Chipper machine feed material typically comprises a number of pieces of logs of differing sizes and shapes. Chipper knives (“knives”) are used to cut the logs as the logs move through the chipper machine. The bearings for chipper machines are of the rolling contact surface type. An anvil is used to hold the logs during the cutting process. A wear plate, including in many cases a replaceable wear plate corner piece, is used to protect the chipper disc from wood pieces and debris associated with the logs.
To ensure that raw material transferred to equipment downstream of the chipper machine is of high quality, the chipper machines must be outfitted with sharp cutting knives, an appropriate wear plate, a replaceable wear plate corner piece, and appropriate anvils. The equipment downstream of the chipper machine includes mechanical refining or chemical refining equipment, or other processes where the chips from the chipper facility are processed to create pulp. It is important in the pulp processing industry for chipper machines to be available and operational with little down time. Chipper machine down time can result from routine maintenance, replacement of the knives used to cut the logs, from checking and replacing wear parts in the chipper machine, such as the wear plate and the anvil, and the replacement of bearings.
As logs move through the chipper machine, the knives cut the logs into chips. In order to obtain chips of a desired size and shape, the anvil is used to position and hold the logs in place while they are being cut by the knives. While efforts are made to feed only logs to the chipper machines, pieces of rock and other debris may also be fed to the chipper machine with the logs. The cutting of both the logs and the associated rocks and debris causes the knives to become dull and damaged, which in turn can result in a poor quality chip. Poor quality chips, including chips of undesired sizes, adversely impact the quality of the pulp produced by downstream processes.
Bearings may become worn or even damaged through normal operation of the chipper machine. One indication of wear or damage may be the audible sounds of the chipper machine. Abnormal bearing sounds can indicate a problem with the bearing and possibly can indicate the severity of the problem. For example, a clang or clatter sound may indicate bearing deformation. Other sounds and the causes are common. One drawback to using sounds to help determine bearing wear or damage is the subjectivity of sounds between people. Another drawback to using sounds to help determine bearing wear or damage is the high level of sound from a chipper machine under routine operations.
It is also possible to use temperature of the bearing to suggest when operational issues occur due to bearing problems. The use of temperature is limited to comparing a temperature to an upper set point of an acceptable temperature for the bearings. Once the upper set point is reached, the chipper machine must be taken offline, inspected, and repaired or replaced.
Another method which can be used to detect damage to bearings is measuring of the vibration of the machine. When vibration measurement is used to detect damage, one must rely on the amplitude and frequency of the vibration to indicate damage to the bearing. The downside of using vibration measurement to detect damage is the values measured differ depending on the operating condition of the bearing and the measuring point of the vibration. As with the previously mentioned possible monitoring practices, the data received is to distinguish problems from normal operations.
Currently, the temperature of the bearing is measured by a sensor. The temperature reading is sent to a computer where the sensed temperature is compared to a maximum allowed temperature. If the sensed temperature is below the maximum allowed temperature, no change is made to the operations. If the sensed temperature is above the maximum allowed temperature, the chipper machine operation is halted, and the chipper machine is inspected and repaired. The current practice is an “on/off” type operation, meaning the chipper machine is either on or the chipper machine is off.
The anvil used to hold the logs may also become damaged and worn by the constant operation of the chipper machine. Also, in addition to the logs and associated rocks and debris comprising the chipper machine feed material, pieces of the knives that have become broken during the cutting of the feed material may hit and damage the anvil. Because poor quality chips may be a result of multiple causes, such as the logs themselves, worn or damaged cutting knives, or anvil wear or damage, the quality of the chips cannot be used to definitively determine whether or not the anvil is worn or damaged. If damage to the anvil is suspected, in conventional applications, the chipper machine must be stopped and the anvil visually inspected. Such inspections may cause unscheduled down time for the chipper machine.
Another part which can become worn for many of the same reasons as the anvil is a wear plate. The wear plate, which may include a replaceable wear plate corner piece bolted to the wear plate, is positioned to protect the chipper disc. As with the anvil, the wear plate, and if present the replaceable wear plate corner piece, may become damaged by the logs, the associated debris fed with the logs, pieces of metal broken off from the cutting knives, or even by the anvil. As previously stated, the quality of the chips may not be an indication of wear or damage to the anvil, the wear plate, or the replaceable wear plate corner piece.
When the anvil, wear plate, or replaceable wear plate corner piece become damaged or worn, an increase in cutting forces exists. As the cutting forces increase, more wear or damage to the wear plate, replaceable wear plate corner piece, and/or anvil may occur. As the wear plate, replaceable wear plate corner piece, and/or anvil become damaged, chip quality suffers. While wear or damage to the wear plate, replaceable wear plate corner piece, or the anvil may cause poor chip quality, other causes of poor chip quality not related to the wear plate, replaceable wear plate corner piece, and the anvil may exist.
There is a long felt need to establish a method to remotely monitor the condition of an anvil, a wear plate, and, when present, a replaceable wear plate corner piece to determine when these parts are damaged or worn and should be replaced. For the bearings, remote monitoring of its condition may involve temperature and vibration and/or force measurements. Such remote monitoring would allow for reduced down time for visual inspection of the anvil, wear plate, or wear replaceable plate corner piece. In the case of bearings, the monitoring based on temperature, vibration and forces may provide information regarding conditions of the bearings and when to schedule inspections and replacement.